Stefan Huber

• PhD
• PostDoc Position at Technical University of Munich

New results are presented on a high-statistics measurement of Collins and Sivers asymmetries of charged hadrons produced in deep inelastic scattering of muons on a transversely polarized LiD 6 target. The data were taken in 2022 with the COMPASS spectrometer using the 160 GeV muon beam at CERN, statistically balancing the existing data on transvers...

The COMPASS Collaboration performed measurements of the Drell-Yan process in 2015 and 2018 using a 190 GeV / c π − beam impinging on a transversely polarized ammonia target. Combining the data of both years, we present final results on the amplitudes of five azimuthal modulations, which correspond to transverse-spin-dependent azimuthal asymmetries...

We present the study of the production of double $J/\psi$ mesons using COMPASS data collected with a 190 GeV/$c$ $\pi^-$ beam scattering off NH$_{3}$, Al and W targets. Kinematic distributions of the collected double $J/\psi$ events are analysed, and the double $J/\psi$ production cross section is estimated for each of the COMPASS targets. The resu...

The Belle II experiment at the SuperKEKB accelerator has started its physics data taking with the full detector setup in March 2019. It aims to collect 40 times more e+e− collision data compared with its predecessor Belle experiment. The Belle II pixel detector (PXD) is based on the Depleted P-channel Field Effect Transistor (DEPFET) technology. Th...

We study the spin-exotic JPC=1−+ amplitude in single-diffractive dissociation of 190 GeV/c pions into π−π−π+ using a hydrogen target and confirm the π1(1600)→ρ(770)π amplitude, which interferes with a nonresonant 1−+ amplitude. We demonstrate that conflicting conclusions from previous studies on these amplitudes can be attributed to different analy...

Based on the observation of sizeable target-transverse-spin asymmetries in single-hadron and hadron-pair production in Semi-Inclusive measurements of Deep Inelastic Scattering (SIDIS), the chiral-odd transversity quark distribution functions h1q are nowadays well established. Several possible channels to access these functions were originally propo...

Triggered data acquisition systems provide only limited possibilities of triggering methods. In our paper, we propose a novel approach that completely removes the hardware trigger and its logic. It introduces an innovative free-running mode instead, which provides unprecedented possibilities to physics experiments. We would like to present such sys...

The COMPASS Collaboration experiment recently discovered a new isovector resonancelike signal with axial-vector quantum numbers, the a1(1420), decaying to f0(980)π. With a mass too close to and a width smaller than the axial-vector ground state a1(1260), it was immediately interpreted as a new light exotic meson, similar to the X, Y, Z states in th...

We study the spin-exotic $J^{PC} = 1^{-+}$ amplitude in single-diffractive dissociation of 190 GeV$/c$ pions into $\pi^-\pi^-\pi^+$ using a hydrogen target and confirm the $\pi_1(1600) \to \rho(770) \pi$ amplitude, which interferes with a nonresonant $1^{-+}$ amplitude. We demonstrate that conflicting conclusions from previous studies on these ampl...

We present a new data acquisition system for the COMPASS++/AMBER experiment designed as a further development of the Intelligent FPGA-based Data Acquisition framework. The system is designed to have a maximum throughput of 5 GB/s. We designed the system to provide free-running continuous readout which allows us to implement a sophisticated data fil...

The SuperKEKB accelerator in Tsukuba, Japan is providing $e^{+}e^{-}$ beams for the Belle II experiment since March 2019. To deal with the aimed peak luminosity being 40 times higher than the one recorded at Belle, a pixel detector based on DEPFET technology has been installed. It features a long integration time of $20~\mu \text {s}$ resulting...

Based on the observation of sizeable target-transverse-spin asymmetries in single-hadron and hadron-pair production in Semi-Inclusive measurements of Deep Inelastic Scattering (SIDIS), the chiral-odd transversity quark distribution functions $h_1^q$ are nowadays well established. Several possible channels to access these functions were originally p...

We report on a measurement of Spin Density Matrix Elements (SDMEs) in hard exclusive $$\omega $$ ω meson muoproduction on the proton at COMPASS using 160 GeV/ c polarised $$ \mu ^{+}$$ μ + and $$ \mu ^{-}$$ μ - beams impinging on a liquid hydrogen target. The measurement covers the range 5.0 GeV/ $$c^2$$ c 2 $$< W<$$ < W < 17.0 GeV/ $$c^2$$ c 2 , w...

The Belle II experiment at the SuperKEKB energy-asymmetric e+e− collider has completed a series of substantial upgrades and started collecting data in 2019. The experiment is expected to accumulate a data set of 50 ab⁻¹ to explore new physics beyond the Standard Model at the intensity frontier. The pixel detector (PXD) of Belle II plays a key role...

In Fig. 5 on p. 311 of our Phys. Lett. B 740 (2015) 303 an adjustment by 180∘ is required for the phases with respect to the L=2,M=1 wave, of the following waves: L=1,3,5 with M=1, and L=2 with M=2. After this correction (Fig. 5 (corrected) below), the extracted partial waves describe the angular distribution of the η(′) in the Gottfried-Jackson (G...

The Belle II experiment features a substantial upgrade of the Belle detector and will operate at the SuperKEKB energy-asymmetric e ⁺ e ⁻ collider at KEK in Tsukuba, Japan. The accelerator completed its first phase of commissioning in 2016, and the Belle II detector saw its first electron-positron collisions in April 2018. Belle II features a newly...

The SuperKEKB accelerator in Tsukuba, Japan is providing e$^+$e$^-$ beams for the Belle II experiment since about two years. To deal with the aimed peak luminosity being forty times higher than the one recorded at Belle, a pixel detector based on DEPFET technology has been installed. It features a long integration time of 20 us resulting in an expe...

We report on a measurement of Spin Density Matrix Elements (SDMEs) in hard exclusive $\omega$ meson muoproduction on the proton at COMPASS using 160 GeV/$c$ polarised $ \mu ^{+}$ and $ \mu ^{-}$ beams impinging on a liquid hydrogen target. The measurement covers the range 5.0 GeV/$c^2$ $< W <$ 17.0 GeV/$c^2$, with the average kinematics $\langle Q^...

The antiparticle-over-particle multiplicity ratio is measured in deep-inelastic scattering for negatively and positively charged kaons and, for the first time, for antiprotons and protons. The data were obtained by the COMPASS Collaboration using a 160 GeV muon beam impinging on an isoscalar ⁶LiD target. The regime of deep-inelastic scattering is e...

The COMPASS experiment recently discovered a new isovector resonance-like signal with axial-vector quantum numbers, the $a_1(1420)$, decaying to $f_0(980)\pi$. With a mass too close to and a width smaller than the axial-vector ground state $a_1(1260)$, it was immediately interpreted as a new light exotic meson, similar to the $X$, $Y$, $Z$ states i...

We report on a measurement of hard exclusive π0 muoproduction on the proton by COMPASS using 160 GeV/c polarised μ+ and μ− beams of the CERN SPS impinging on a liquid hydrogen target. From the average of the measured μ+ and μ− cross sections, the virtual-photon proton cross section is determined as a function of the squared four-momentum transfer b...

Hadron leptoproduction in Semi-Inclusive measurements of Deep-Inelastic Scattering (SIDIS) on unpolarised nucleons allows one to get information on the intrinsic transverse momentum of quarks in a nucleon and on the Boer-Mulders function through the measurement of azimuthal modulations in the cross section. These modulations were recently measured...

The original version of this article unfortunately contained a mistake.

The $\bar{\rm p} $ over p multiplicity ratio is measured in deep-inelastic scattering for the first time using (anti-) protons carrying a large fraction of the virtual-photon energy, $z>0.5$. The data were obtained by the COMPASS Collaboration using a 160 GeV muon beam impinging on an isoscalar $^6$LiD target. The regime of deep-inelastic scatterin...

In HEP experiments, remote access to control systems is one of the fundamental pillars of efficient operations. At the same time, development of user interfaces with emphasis on usability can be one of the most labor-intensive software tasks to be undertaken in the life cycle of an experiment. While desirable, the development and maintenance of a l...

On March 25th 2019, the Belle II detector recorded the first collisions delivered by the SuperKEKB accelerator. This marked the beginning of the physics run with vertex detector. The vertex detector was aligned initially with cosmic ray tracks without magnetic field simultaneously with the drift chamber. The alignment method is based on Millepede I...

Hadron leptoproduction in Semi-Inclusive measurements of Deep-Inelastic Scattering (SIDIS) on unpolarised nucleons allows one to get information on the intrinsic transverse momentum of quarks in a nucleon and on the Boer-Mulders function through the measurement of azimuthal modulations in the cross section. These modulations were recently measured...

In addition to the common 3-body decay of the neutron $n\rightarrow p e^-\overline{\nu_e}$ there should exist an effective 2-body subset with the electron and proton forming a Hydrogen bound state with well defined total momentum, total spin and magnetic quantum numbers. The atomic spectroscopic analysis of this bound system can reveal details abou...

A DEpleted P-channel Field Effect Transistor (DEPFET) based pixel detector was developed for the Belle II VerteX Detector (VXD). It is designed to achieve a good impact parameter resolution better than 15μm at the very high luminosity conditions of this experiment. In the first half of 2018 four final production modules have been deployed in the co...

We report on the first measurement of exclusive single-photon muoproduction on the proton by COMPASS using 160 GeV/c polarised μ ⁺ and μ ⁻ beams of the CERN SPS impinging on a liquid hydrogen target. We determine the dependence of the average of the measured μ ⁺ and μ ⁻ cross sections for deeply virtual Compton scattering on the squared four-moment...

We report on a measurement of hard exclusive $\pi^0$ muoproduction on the proton by COMPASS using 160 GeV/$c$ polarised $\mu^+$ and $\mu^-$ beams of the CERN SPS impinging on a liquid hydrogen target. From the average of the measured $\mu^+$ and $\mu^-$ cross sections, the virtual-photon proton cross section is determined as a function of the squar...

Recently, a stability of Data Acquisition System (DAQ) has become a vital precondition for a successful data taking in high energy physics experiments. The intelligent, FPGA-based Data Acquisition System (iFDAQ) of the COMPASS experiment at CERN is designed to be able to readout data at the maximum rate of the experiment and runsin a mode without a...

Modern experiments demand a powerful and efficient Data Acquisition System (DAQ). The intelligent, FPGA-based Data Acquisition System (iFDAQ) of the COMPASS experiment at CERN is composed of many processes communicating between each other. The DIALOG library covers a communication mechanism between processes and establishes a communication layer to...

The transverse spin asymmetries measured in semi-inclusive leptoproduction of hadrons, when weighted with the hadron transverse momentum PT, allow for the extraction of important transverse-momentum-dependent distribution functions. In particular, the weighted Sivers asymmetries provide direct information on the Sivers function, which is a leading-...

We have performed the most comprehensive resonance-model fit of π−π−π+ states using the results of our previously published partial-wave analysis (PWA) of a large data set of diffractive-dissociation events from the reaction π−+p→π−π−π++precoil with a 190 GeV/c pion beam. The PWA results, which were obtained in 100 bins of three-pion mass, 0.5<m3π<...

Single hadron azimuthal asymmetries of positive and negative hadrons produced in muon semi-inclusive deep inelastic scattering off longitudinally polarised deuterons are determined using the 2006 COMPASS data and also combined all deuteron COMPASS data. For each hadron charge, the dependence of the azimuthal asymmetry on the hadron azimuthal angle...

The K⁻ over K⁺ multiplicity ratio is measured in deep-inelastic scattering, for the first time for kaons carrying a large fraction z of the virtual-photon energy. The data were obtained by the COMPASS collaboration using a 160 GeV muon beam and an isoscalar ⁶LiD target. The regime of deep-inelastic scattering is ensured by requiring Q²>1(GeV/c)² fo...

The transverse spin asymmetries measured in semi-inclusive leptoproduction of hadrons, when weighted with the hadron transverse momentum $P_T$, allow for the extraction of important transverse-momentum-dependent distribution functions. In particular, the weighted Sivers asymmetries provide direct information on the Sivers function, which is a leadi...

We have searched for exclusive production of exotic charmonia in the reaction μ⁺N→μ⁺(J/ψπ⁺π⁻)π±N′ using COMPASS data collected with incoming muons of 160 GeV/c and 200 GeV/c momentum. In the J/ψπ⁺π⁻ mass distribution we observe a signal with a statistical significance of 4.1 σ. Its mass and width are consistent with those of the X(3872). The shape...

We present a new amplitude analysis of the ηπ D-wave in the reaction π⁻p→ηπ⁻p measured by COMPASS. Employing an analytical model based on the principles of the relativistic S-matrix, we find two resonances that can be identified with the a2(1320) and the excited a2′(1700), and perform a comprehensive analysis of their pole positions. For the mass a...

We present a precise measurement of the proton longitudinal double-spin asymmetry A1p and the proton spin-dependent structure function g1p at photon virtualities 0.006(GeV/c)2<Q2<1(GeV/c)2 in the Bjorken x range of 4×10−5<x<4×10−2. The results are based on data collected by the COMPASS Collaboration at CERN using muon beam energies of 160GeV and 20...

We have performed the most comprehensive resonance-model fit of $ \pi^-\pi^-\pi^+$ states using the results of our previously published partial-wave analysis (PWA) of a large data set of diffractive-dissociation events from the reaction $\pi^- + p \to \pi^-\pi^-\pi^+ + p_{recoil}$ with a 190 GeV/${\it c}$ pion beam. The PWA results, which were obta...

We report on the first measurement of exclusive single-photon muoproduction on the proton by COMPASS using 160 GeV/$c$ polarized $\mu^+$ and $\mu^-$ beams of the CERN SPS impinging on a liquid hydrogen target. We determine the dependence of the average of the measured $\mu^+$ and $\mu^-$ cross sections for deeply virtual Compton scattering on the s...

A semi-inclusive measurement of charged hadron multiplicities in deep inelastic muon scattering off an isoscalar target was performed using data collected by the COMPASS Collaboration at CERN. The following kinematic domain is covered by the data: photon virtuality Q2>1 (GeV/c)2, invariant mass of the hadronic system W>5 GeV/c2, Bjorken scaling var...

The K$^{-}$ over K$^{+}$ multiplicity ratio is measured in deep-inelastic scattering, for the first time for kaons carrying a large fraction $z$ of the virtual-photon energy. The data were obtained by the COMPASS collaboration using a 160 GeV muon beam and an isoscalar $^6$LiD target. The regime of deep-inelastic scattering is ensured by requiring...

We present a precise measurement of the proton longitudinal double-spin asymmetry $A_1^{\rm p}$ and the proton spin-dependent structure function $g_1^{\rm p}$ at photon virtualities $0.006~({\rm GeV}/c)^2<Q^2 < 1~({\rm GeV}/c)^2$ in the Bjorken $x$ range of $4 \times 10^{-5} < x < 4 \times 10^{-2}$. The results are based on data collected by the CO...

A semi-inclusive measurement of charged hadron multiplicities in deep inelastic muon scattering off an isoscalar target was performed using data collected by the COMPASS Collaboration at CERN. The following kinematic domain is covered by the data: photon virtuality $Q^{2}>1$ (GeV/$c$)$^2$, invariant mass of the hadronic system $W > 5$ GeV/$c^2$, Bj...

The first measurement of transverse-spin-dependent azimuthal asymmetries in the pion-induced Drell-Yan (DY) process is reported. We use the CERN SPS 190 GeV/c π− beam and a transversely polarized ammonia target. Three azimuthal asymmetries giving access to different transverse-momentum-dependent (TMD) parton distribution functions (PDFs) are extrac...

The Unified Communication Framework is an unified network protocol and FPGA core for high speed serial interfaces employed in Data Acquisition systems. It provides up to 64 different communication channels via a single serial link. One channel is reserved for timing and trigger information whereas the other channels can be used for slow control int...

We present a new amplitude analysis of the $\eta\pi$ $D$-wave in $\pi^- p\to \eta\pi^- p$ measured by COMPASS. Employing an analytical model based on the principles of the relativistic $S$-matrix, we find two resonances that can be identified with the $a_2(1320)$ and the excited $a_2^\prime(1700)$, and perform a comprehensive analysis of their pole...

We have observed exclusive production of the exotic $X(3872)$ hadron in the reaction $\mu^+~N \rightarrow \mu^+ (J\!/\!\psi\pi^+\pi^-)\pi^{\pm}~N'$ using COMPASS data collected with incoming muons of 160~GeV/$c$ and 200~GeV/$c$ momentum. The statistical significance of the $X(3872)$ signal is 6$\sigma$. The shape of the two-pion mass distribution s...

The Sivers function describes the correlation between the transverse spin of a nucleon and the transverse motion of its partons. For quarks, it was studied in previous measurements of the azimuthal asymmetry of hadrons produced in semi-inclusive deep inelastic scattering of leptons off transversely polarised nucleon targets, and it was found to be...

In this paper we present the FPGA-based framework IFDAQ which is used for the development of data acquisition systems for detectors in high energy physics. The framework supports Xilinx FPGA and provides a collection of IP cores written in VHDL which use the common interconnect interface. The IP core library offers functionality required for the de...

The first measurement of transverse-spin-dependent azimuthal asymmetries in the pion-induced Drell-Yan (DY) process is reported. We use the CERN SPS 190 GeV/$c$, $\pi^{-}$ beam and a transversely polarized ammonia target. Three azimuthal asymmetries giving access to different transverse-momentum-dependent (TMD) parton distribution functions (PDFs)...

Eight proton transverse-spin-dependent azimuthal asymmetries are extracted in four regions of the photon virtuality Q2 from the COMPASS 2010 semi-inclusive hadron measurements in deep inelastic muon-nucleon scattering. These Q2 regions correspond to the four regions of the di-muon mass Q2 used in the ongoing analyses of the COMPASS Drell-Yan measur...

Final results are presented from the inclusive measurement of deep-inelastic polarised-muon scattering on longitudinally polarised deuterons using a ⁶LiD target. The data were taken at 160 GeV beam energy and the results are shown for the kinematic range in photon virtuality, in the Bjorken scaling variable and in the mass of the hadronic final sta...

The COMPASS collaboration has collected the currently largest data set on diffractively produced π−π−π+ final states using a negative pion beam of 190 GeV/c momentum impinging on a stationary proton target. This data set allows for a systematic partial-wave analysis in 100 bins of three-pion mass, 0.5<m3π<2.5 GeV/c2, and in 11 bins of the reduced f...

Using a novel analysis technique, the gluon polarisation in the nucleon is re-evaluated using the longitudinal double-spin asymmetry measured in the cross section of semi-inclusive single-hadron muoproduction with photon virtuality \(Q^2>1~(\mathrm{GeV}/c)^2\). The data were obtained by the COMPASS experiment at CERN using a 160 GeV/c polarised muo...

The Sivers function describes the correlation between the transverse spin of a nucleon and the transverse motion of its partons. It was extracted from measurements of the azimuthal asymmetry of hadrons produced in semi-inclusive deep inelastic scattering of leptons off transversely polarised nucleon targets, and it turned out to be non-zero for qua...

We present a new amplitude analysis of the $\eta\pi$ $D$-wave in $\pi^- p\to \eta\pi^- p$ measured by COMPASS. Employing an analytical model based on the principles of the relativistic $S$-matrix, we find two resonances that can be identified with the $a_2(1320)$ and the excited $a_2^\prime(1700)$, and perform a comprehensive analysis of their pole...

Final results are presented from the inclusive measurement of deep-inelastic polarised-muon scattering on longitudinally polarised deuterons using a $^6$LiD target. The data were taken at $160~{\rm GeV}$ beam energy and the results are shown for the kinematic range $1~({\rm GeV}/c)^2 < Q^2 < 100~({\rm GeV}/c)^2$ in photon virtuality, $0.004<x<0.7$...

Proton transverse-spin azimuthal asymmetries are extracted from the COMPASS 2010 semi-inclusive hadron measurements in deep inelastic muon-nucleon scattering in those four regions of the photon virtuality $Q^2$, which correspond to the four regions of the di-muon mass $\sqrt{Q^2}$ used in the ongoing analysis of the COMPASS Drell-Yan measurements....

Single hadron azimuthal asymmetries in the cross sections of positive and negative hadron production in muon semi-inclusive deep inelastic scattering off longitudinally polarised deuterons are determined using the 2006 COMPASS data and also all deuteron COMPASS data. For each hadron charge, the dependence of the azimuthal asymmetry on the hadron az...

Precise measurements of charged-kaon multiplicities in deep inelastic scattering were performed. The results are presented in three-dimensional bins of the Bjorken scaling variable x, the relative virtual-photon energy y, and the fraction z of the virtual-photon energy carried by the produced hadron. The data were obtained by the COMPASS Collaborat...

Precise measurements of charged-kaon multiplicities in deep inelastic scattering were performed. The results are presented in three-dimensional bins of the Bjorken scaling variable x, the relative virtual-photon energy y, and the fraction z of the virtual-photon energy carried by the produced hadron. The data were obtained by the COMPASS Collaborat...

Exclusive production of $\omega$ mesons was studied at the COMPASS experiment by scattering $160~\mathrm{GeV}/\mathit{c}$ muons off transversely polarised protons. Five single-spin and three double-spin azimuthal asymmetries were measured in the range of photon virtuality $1~(\mathrm{GeV}/\mathit{c})^2 < Q^2 < 10~(\mathrm{GeV}/\mathit{c})^2$, Bjork...

Exclusive production of $\omega$ mesons was studied at the COMPASS experiment by scattering $160~\mathrm{GeV}/\mathit{c}$ muons off transversely polarised protons. Five single-spin and three double-spin azimuthal asymmetries were measured in the range of photon virtuality $1~(\mathrm{GeV}/\mathit{c})^2 < Q^2 < 10~(\mathrm{GeV}/\mathit{c})^2$, Bjork...

In this paper we present the FPGA-based framework IFDAQ which is used for the development of the data acquisition systems for detectors in high energy physics. The framework supports Xilinx FPGA and provides a collection of the IP cores written in VHDL which use the common interconnect interface. The IP core library offers functionality required fo...

The Unified Communication Framework is a unified network protocol and FPGA firmware for high speed serial interfaces employed in Data Acquisition systems. It provides up to 64 different communication channels via a single serial link. One channel is reserved for timing and trigger information whereas the other channels can be used for slow control...

Multiplicities of charged pions and unidentified hadrons produced in deep-inelastic scattering were measured in bins of the Bjorken scaling variable $x$, the relative virtual-photon energy $y$ and the relative hadron energy $z$. Data were obtained by the COMPASS Collaboration using a 160 GeV muon beam and an isoscalar target ($^6$LiD). They cover t...

Multiplicities of charged pions and unidentified hadrons produced in deep-inelastic scattering were measured in bins of the Bjorken scaling variable $x$, the relative virtual-photon energy $y$ and the relative hadron energy $z$. Data were obtained by the COMPASS Collaboration using a 160 GeV muon beam and an isoscalar target ($^6$LiD). They cover t...

This paper presents development and recent status of the new data acquisiton system of the COMPASS experiment at CERN with up to 50 kHz trigger rate and 36 kB average event size during 10 second period with beam followed by approximately 40 second period without beam. In the original DAQ, the event building is performed by software deployed on swit...

COMPASS is a fixed-target experiment at the SPS at CERN dedicated to the study of hadron structure and spectroscopy. Since 2014, a hardware event builder consisting of nine custom designed FPGA-cards replaced the previous online computers increasing compactness and scalability of the DAQ. By buffering data, the system exploits the spill structure o...